Will resource packs for 1.16.4+ work on older versions?

Question

I'm making a texture pack but I don't want to make an entirely new pack for older versions.

Answer 1

They should, I wouldn't see why it would cause an issue. Might look weird because of the old update they did to textures a few updates back.

Answer 2

Depends on Texture Pack. Some might, some might not. This is due to the fact that different versions use different coding and / or Item IDs.
For example, a 1.16 Custom Items pack won't work on 1.12.2 and some other versions because of the CIT(Custom Item Texture) coding difference & Item ID changes.